1. Field of the Invention
The present invention relates to a cooling apparatus for arrangement between two surface coils of a gradient coil for dissipating the heat produced when supplying current to the surface coils by means of a coolant flowing into the cooling apparatus.
2. Description of the Prior Art
Gradient coils for magnetic resonance devices essentially include triaxial magnetic field coils, which are cast in a resin matrix (usually epoxy resin), in order to produce the desired mechanical and electrical properties of the coil. The magnetic field coils are usually designed as surface coils having a carrier, onto which the coil conductors are applied and/or wound in a predetermined pattern. These surface coils are bent in order to produce the conventionally cylindrical gradient coils, generally describing a partial circle of a little less than 180°.
The surface coils are supplied with current in order to generate the gradient fields. Gradient currents of several hundred amperes with electrical voltages up to 2 kV are usual and result in power losses of usually >10 kW in the form of heat, which must be dissipated. For this purpose, each gradient coil has a cooling apparatus. In order to be able to dissipate the power as efficiently as possible, cooling tubes forming the cooling apparatus are embedded in the resin between the individual surface coils, which lie relatively closely together, with several 100 m of cooling tube per surface coil typically being provided as well as several parallel cooling circuits. The insertion and/or winding of the cooling tubes is very complex and time-consuming, because the cooling tubes are wound onto a supporting plate by hand and are fixed with waxed silk cords in through-holes in the supporting plate, with the tube ends being positioned directly adjacent to one another for the water inlet and outlet. It is furthermore disadvantageous that excessively narrow radii cannot be wound with a cooling tube typically in the form of a polyamide pipe, having an external diameter of 8 mm with a wall thickness of 1 mm, without risking excessive cross-sectional narrowing or the formation of a kink, sometimes resulting in zones which cannot be covered with a cooling tube.